The invention relates to an electromechanical stabilizer for the chassis of a vehicle, particularly a motor vehicle, having an actuator, which is integrated between two stabilizer halves and, as required, rotates the latter with respect to one another by a rotation angle. The actuator consists of an electric motor, as well as a transmission connected to the output side of this electric motor. With respect to the technical environment, reference is made, for example, to German patent document DE 44 43 809 A1.
By means of a motor vehicle chassis whose stabilizer is divided into a first stabilizer half assigned to the suspension of the left wheel of a vehicle axle and into a second stabilizer half assigned to the suspension of the right wheel of this vehicle axle, and, in the case of which, these stabilizer halves can be rotated with respect to one another about their joint longitudinal axis, a clearly increased vehicle roll stability can be achieved in comparison to chassis having a one-piece stabilizer. In this case, a suitable oscillating motor or general actuator is provided between the two stabilizer halves which, on the basis of a suitable control, as required, rotates these stabilizer halves with respect to one another. This oscillating motor or actuator is constructed in the above mentioned patent document in the form of a hydraulic rotary drive.
Instead of a hydraulic rotary drive, an electromechanical actuator may be provided, which comprises an electric motor and a mechanical transmission as well as a locking brake. This results in a so-called electromechanical stabilizer consisting of the two stabilizer halves, which are connected with one another by an electromechanical actuator. As described above, this electromechanical actuator also has the purpose of achieving a rotation of the two stabilizer halves with respect to one another in a targeted manner, so that a desired stabilizer torque is generated which will then prevent a rolling of the vehicle body.
As illustrated in a simplified manner in FIG. 1, an electromechanical actuator internally known to the assignee of the present invention is marked with the reference number 1 and, as mentioned above, comprises an electric motor 2 and a mechanical transmission 3 as well as a locking brake 4. The selected transmission ratio of the transmission 3, which is preferably constructed as a three-stage planetary gear transmission, is constant. The dynamics of the overall system are decisively characterized by the transmission ratio, the inertia of the masses of the system and the resistance to torsion of the two stabilizer halves provided with the reference numbers 5a and 5b. The above-mentioned locking brake 4 is required for protecting the electric motor 2 against overload as a result of high stabilizer torques.
Electric motors are normally characterized by high rotational speeds and low nominal torques and are not particularly suitable per se for the present use in an electromechanical stabilizer. The reason for this is that the electromechanical actuator should generate high torques in this case while the angles of rotation are small. This contradiction necessarily results in a high transmission ratio for the required transmission, which, however, also has disadvantages. It therefore results not only in a large size (because of the required planetary stages) but also in a relatively low efficiency (because of the unavoidable friction losses). As a function of the respective usage, torques must be implemented on the stabilizer which are so high that the high transmission ratios required for this purpose cannot be implemented at all because the available space, as well as the efficiency, define an upper physical limit.
Furthermore, a high transmission ratio has a negative effect on the dynamics of the overall system. The reason is that the natural frequency of the system is inversely proportional to the transmission ratio. This is a result of the wheel-related inertia of the masses, which is defined from the actuator inertia multiplied by the squared wheel-related transmission ratio (this is the ratio between the angle of rotation of the electric motor and the resulting wheel lift). As a result, a negative influence is exercised on the driving comfort and the energy consumption of the overall system.
It is an object of the present invention to provide a remedial measure for these described problems. This object is achieved in that the transmission has a transmission ratio which changes as a function of the angle of rotation. Advantageous developments and further developments are described herein and contained in the subclaims.